Drive units of the foregoing type have been known for quite some time. They are double-axle drives which are also indentified as floating drives. German Patent No. 838 452 has as its subject matter a drive of the described type, in which the elastic coupling is formed by a rubber disk which surrounds the wheel-set axle and which is connected on one side, for example by vulcanizing, to a disk-shaped flange which is secured on the hollow shaft and is connected on its other side to a disk-shaped flange which is mounted on the wheel-set axle. (Where reference is made herein to rubber, then plastics and similar materials which have characteristics comparable to rubber are also included.) Due to the weight of the drive unit and the mass forces which occur during operation, the rubber disks are mainly stressed for thrust, namely in a plane which lies perpendicular to the wheel-set axle. In order to thereby not permit the drive unit to sag too much with respect to the wheel-set axle, the rubber disks must be relatively narrow and hard. With this, however, the negative effects of the tangential stress are increased and the spring action in a transverse direction, namely in the direction of the wheel-set axle, is further degraded. A further very important disadvantage is that, during replacement of the rubber disks when replacement becomes necessary, the wheels must be pulled off the axles.
This operationally disturbing disadvantage is avoided in a coupling with split rubber elements, as is known for example from German Offenlegungsschrift No. 23 32 281. A hub which is mounted on the hollow shaft and a hub which is mounted on the wheel-set axle each have a number of arms which extend radially outwardly and are arranged alternately, one after the other. A rubber block is inserted between each pair of arms. The rubber blocks can each be removed radially outwardly and can be installed from the outside without pulling the wheels off the axles, but special devices are needed for installing and removing rubber blocks. This type of coupling is very stiff in the plane which is perpendicular to the wheel-set axle. It is softer in a transverse direction than the design with the rubber disks, but the rubber blocks are exposed to a tangential stress. A further disadvantage is the fact that the rubber blocks receive their initial tension only during installation, which also makes installing and removing them difficult.
Also, a coupling has been suggested for those cases of use (German Offenlegungsschrift No. 28 53 839) in which two coupling halves, one of which is mounted on the hollow shaft of the gearing and the other on the wheel-set axle, are both constructed substantially as rotation-symmetric members, and are connected with one another by radially arranged rubber-joint sleeves. In this design, even though the installing and removing of the rubber-joint sleeves can be carried out easily, their dimensioning does pose some problems in order to be able to fulfill as completely as possible all requirements.
In all mentioned existing designs, the elastic couplings between the hollow shafts and the wheel-set axles have the task to support the motor-gearing unit on the wheel-set axle and to also transmit the driving torque onto the wheel-set axle. The restoring forces which, during an angular deflection of the wheel-set axle, act from the elastic coupling onto the wheel-set axle are thereby supposed to be as small as possible. The reason for this is that, during travelling over unevennesses (for example switches and crossings) or obstacles (for example small articles lying on the rails) which cause one of the four wheels to drop down one-sidedly or to be lifted up, an unfavorable influence on the wheel forces is avoided as much as possible and in this manner the safety against derailing is not influenced.
A drive unit of the general type to which the invention relates is known from German Auslegeschrift No. 24 34 420. In this arrangement of the motor-gearing unit in the vehicle or bogie frame, the elastic coupling transmits between the gearing unit hollow shaft and the wheel-set axle only torques, but the motor-gearing unit is, in spite of the use of elastic bearing sleeves, relatively rigid. If one desires to arrange the motor-gearing unit so as to be substantially cushioned, then solutions are available as used in the aforedescribed double longitudinal drives. In the known designs, one tries to do justice as much as possible to the set demands through a specific construction of the couplings and the elastic elements contained therein. This, however, is only possible in the form of compromises. The demand for high stiffness in a radial direction and in a peripheral direction (with reference to the wheel-set axle), and for a very small stiffness during an angular deflection of the wheel-set axle relative to the hollow shaft, have so far been met only incompletely. In the design according to German Offenlegungsschrift No. 23 32 281, for example, the relationship to each other of the stiffnesses which act in various directions and the stress of the elastic elements was improved over the design according to German Patent No. 838 452. However, the disadvantageous dependency of these values from one another remains, so that only a compromise is possible. For example, during an angular deflection of the wheel-set axle in a vertical plane, the elastic elements which just then lie in the horizontal plane are stressed for pressure and are thus relatively stiff. If one would make the elastic elements softer in this pressure direction in order to achieve a more favorable characteristic line, then automatically "softer" characteristic lines in a radial direction and in a peripheral direction would also result, which is contrary to the initially mentioned demands. Furthermore, a higher stress of the elastic elements would also result.
To do away with the mentioned disadvantages in order to indeed fulfill the mentioned demands in a basic purpose of the present invention.